1. Field of the Invention
The present invention relates generally to solid rocket propellants, and in particular to higher-performance solid-rocket propellants and methods of utilizing them.
2. Description of the Related Art
High performance is a relative term, as one of the highest performing extruded propellant in use is HEN-12, which substantially is a cartridge-loaded solid-propellant charge extruded from bulk thermoplastic double-base (DB; gelatinized, polymeric nitrocellulose-nitroglycerin) composition. For propellants of this class, the binder volume-fraction (Φb) approaches 100% binder, as the propellant is also the binder. Achievement of yet higher-performing propellant requires filling the composition (i.e.; replacing a proportion of the polymeric propellant volume) with selected solid fillers (e.g.; metallic fuels, oxidizers, nitramines and the like), thereby yielding a class of propellants categorized as “composite-modified double-base” (CMDB). For several reasons, CMDB compositions having a high solids volume-fraction (Φs) are problematic to extrude. The disclosed invention teaches compositions and methods for utilizing these higher-performing compositions.
CMDB compositions are employed when more energy is needed for a finite volume, either to achieve higher rocket velocities or to deliver larger ammunition payloads. The energy, or more precisely, the energy density is defined as the Figure of Merit (FM), where FM is the impulse per unit mass times the density, which is equivalent to the impulse per volume. The impulse is the integral of the force times time or the derivative of momentum with respect to time. As stated in the previous paragraph, in order to achieve propellants having a higher Figure of Merit requires filling the composition with metallic fuels, oxidizers, nitramines, and the like, and these modified propellants are problematic if extruded. The filled composition typically has a significantly higher viscosity, and if it can be extruded, the propellant usually exhibits phase-separation and/or knit-lines that poorly re-join and re-knit. Phase-separation and/or knit-lines are evidence of anisotropic or orthotropic orientation, which can lead to disastrous consequences when the rocket is launched. The CMDB compositions are typically cast, but there are problems with casting, as a thermosetting binder or the like has to be added back into the composition. Another processing method is die compaction using a die press, but again there is anisotropic or orthotropic orientation, versus the desirable isotropic orientation.
What is needed is a higher-performing propellant, which can be formed into high L/D ratio rocket motors, where the resulting motor is a nearly isotropic material (e.g. substantially free of anisotropic and orthotropic orientation).